1. Field of the Invention
This invention relates to photometry devices that measure the brightness of an object, and more particularly, to photometry devices suitable for use in automatic exposure control of a camera.
2. Description of Related Art
FIG. 13 is a block diagram showing one example of a prior art photometry device (Japanese Laid-Open Patent Application No. 57-131178, which corresponds to U.S. Pat. Nos. 4,479,062 and 4,544,848). A saturation sensor 52 senses whether the output of a photometric circuit (which includes a photoelectric conversion element 51) is saturated. When saturated, sensor 52 switches a switch 53, which reverses the output of a comparator 54. This causes a clock generator 55 to generate clock pulses such that the accumulation time of the photoelectric conversion element 51 is shortened.
The photometry device described above detects whether the output of the photoelectric conversion element 51 is saturated using the saturation sensor 52. However, the saturation sensor 52 cannot determine whether the output is normal or abnormal. For example, depending upon the construction of the photoelectric conversion element, when 100 (or more) times the allowable amount of light enters the photoelectric conversion element, the output passes through a state of saturation and then begins to decrease, resulting in the so-called inversion effect. When this inversion effect occurs, because the output value becomes less than in the state of saturation, the photoelectric conversion element 51 continues to output erroneous photometric information without the saturation sensor 52 being able to sense the abnormality of the output.